PCF8574A: issue while communicating with IC

The schematic is missing.

The address of the PCF8574A is 0111xxx. That waveform does not appear to match.

Hello Clenmens,

Please check Schematic

Again, the waveform does not look like the correct address. (But it would be necessary to see SCL and SDA at the same time to confirm.)

Also check that your I²C pins are configured as open drain.

Hi Clemens,

when i use same code and put external i2c expander, with address 0x20 i.e. for external expander module. it works good.

External i2c expander is connected with same pins with some test points on PCBA.

The PCF8574A does not have address 0x20.

Hi Naresh,

As Clemen's pointed out. The PCF8574A cannot have an address 0x20h. The non-A variant can which I'm assuming you may be using by accident if your device is responding to an address of 0x20h.

-Bobby

Hi Bobby,

I have tried with address 0x70, as mentioned in device datasheet as well., but not working for 0x70

We do not know whether your unknown microcontroller uses 8-bit or 7-bit addresses; try 0x38.

Naresh,

It may also help if you're able to get the SDA/SCL signals on the same scope capture when the device ACKs.

I suggest we also confirm what the top marking on the device is.

-Bobby